Biomedical Engineering Reference
In-Depth Information
These differences result from the inhomogeneity of the environmental
stimulus. As the transverse pressure is loaded, an inhomogeneous strain
field is generated, which results in the inhomogeneous distribution of the
environmental stimulus. The quantity of growth factors released to the bone
fluid then varies in different areas of the bone structure. As the environmen-
tal stimulus decreases due to the bone remodeling process, the inhomoge-
neity disables the bone tissues in different areas of the bone structure from
reaching the MESm at the same time. This means that the bone tissue in
some areas of the bone cannot excrete excess growth factors (i.e., redundant
growth factors after the refilling process) to deposit additional bone material
because the environmental stimulus is within the remodeling range.
However, additional growth factors can still be generated in the remaining
areas at the same time, and new bone material deposition will continue until
all of the bone tissues return to the remodeling mode. The amount of bone
tissue in the remodeling state will then diminish as the bone remodeling
process goes on. Thus, the gradual divergence of internal bone remodeling
and the rate change of surface remodeling can be easily understood. The
reversal of the surface remodeling rate occurs when some of the bone tissue
reverts to the remodeling mode. In the case of axial loading, the environmen-
tal stimulus is distributed homogeneously, which means that all of the bone
tissue can revert to the remodeling mode at the same time, and internal and
surface remodeling cease simultaneously. However, in this case, when sur-
face remodeling ceases, not all of the bone tissue stops excreting additional
growth factors. Internal bone remodeling will continue until all of the bone
tissue is in the remodeling mode. Thus, the surface and internal remodeling
cease at different times. It should be mentioned that, as we assumed before,
growth factors can be homogeneously distributed in bone structure due to
the flow of bone fluid, so a homogeneous bone structure is maintained.
5.5.2.3 Effect of an Electrical Field on Bone Remodeling Process
As earlier investigations have shown that the influences of electrical and
magnetic fields are similar [2,66], we here consider only the electrical field.
The results are shown in Figures 5.14 and 5.15. The applied loadings are
P
= 1.2 kN, φ = 5, 10, 15, 20, 25 V,
f
e
= 2 Hz, and no other loadings are applied;
here, φ = φ
b
− φ
a
.
Figures 5.14 and 5.15 show the effect of electrical loading on the internal
and surface bone remodeling process. It can be seen that as the electrical
loading increases to a certain level, bone remodeling can be triggered. An
electrical field can model the bone structure to fit its environment so that
the loading does not break or harm it. Electrical fields can also make bone
structure stronger and denser and increase the cross-sectional area of bone
and make it thicker. The change rates increase as the intensity of the loading
increases. All these features are effective methods to return a bone structure
to the remodeling mode.
